Overview¶

The CXL spec defines a set of commands that can be issued to the mailbox of aCXL device or switch. It also left room for vendor specific commands to beissued to the mailbox as well. fwctl provides a path to issue a set of allowedmailbox commands from user space to the device moderated by the kernel driver.

The following 3 commands will be used to support CXL Features:CXL spec r3.1 8.2.9.6.1 Get Supported Features (Opcode 0500h)CXL spec r3.1 8.2.9.6.2 Get Feature (Opcode 0501h)CXL spec r3.1 8.2.9.6.3 Set Feature (Opcode 0502h)

The “Get Supported Features” return data may be filtered by the kernel driver todrop any features that are forbidden by the kernel or being exclusively used bythe kernel. The driver will set the “Set Feature Size” of the “Get SupportedFeatures Supported Feature Entry” to 0 to indicate that the Feature cannot bemodified. The “Get Supported Features” command and the “Get Features” fallsunder the fwctl policy of FWCTL_RPC_CONFIGURATION.

For “Set Feature” command, the access policy currently is broken down into twocategories depending on the Set Feature effects reported by the device. If theSet Feature will cause immediate change to the device, the fwctl access policymust be FWCTL_RPC_DEBUG_WRITE_FULL. The effects for this level are“immediate config change”, “immediate data change”, “immediate policy change”,or “immediate log change” for the set effects mask. If the effects are “configchange with cold reset” or “config change with conventional reset”, then thefwctl access policy must be FWCTL_RPC_DEBUG_WRITE or higher.

fwctl cxl User API¶

structfwctl_rpc_cxl¶

ioctl(FWCTL_RPC) input for CXL

struct fwctl_rpc_cxl {    __u32 opcode;    __u32 flags;    __u32 op_size;    __u32 reserved1;    union {        struct cxl_mbox_get_sup_feats_in get_sup_feats_in;        struct cxl_mbox_get_feat_in get_feat_in;        struct cxl_mbox_set_feat_in set_feat_in;    };};

structfwctl_rpc_cxl_out¶

ioctl(FWCTL_RPC) output for CXL

struct fwctl_rpc_cxl_out {    __u32 size;    __u32 retval;    union {        struct cxl_mbox_get_sup_feats_out get_sup_feats_out;        __u8 payload[];    };};

staticintcxl_fwctl_rpc_get_test_feature(intfd,structtest_feature*feat_ctx,constuint32_texpected_data){structcxl_mbox_get_feat_in*feat_in;structfwctl_rpc_cxl_out*out;structfwctl_rpcrpc={0};structfwctl_rpc_cxl*in;size_tout_size,in_size;uint32_tval;void*data;intrc;in_size=sizeof(*in)+sizeof(*feat_in);rc=posix_memalign((void**)&in,16,in_size);if(rc)return-ENOMEM;memset(in,0,in_size);feat_in=&in->get_feat_in;uuid_copy(feat_in->uuid,feat_ctx->uuid);feat_in->count=feat_ctx->get_size;out_size=sizeof(*out)+feat_ctx->get_size;rc=posix_memalign((void**)&out,16,out_size);if(rc)gotofree_in;memset(out,0,out_size);in->opcode=CXL_MBOX_OPCODE_GET_FEATURE;in->op_size=sizeof(*feat_in);rpc.size=sizeof(rpc);rpc.scope=FWCTL_RPC_CONFIGURATION;rpc.in_len=in_size;rpc.out_len=out_size;rpc.in=(uint64_t)(uint64_t*)in;rpc.out=(uint64_t)(uint64_t*)out;rc=send_command(fd,&rpc,out);if(rc)gotofree_all;data=out->payload;val=le32toh(*(__le32*)data);if(memcmp(&val,&expected_data,sizeof(val))!=0){rc=-ENXIO;gotofree_all;}free_all:free(out);free_in:free(in);returnrc;}

fwctl cxl Kernel API¶

intdevm_cxl_setup_features(structcxl_dev_state*cxlds)¶

Allocate and initialize features context

structcxl_features_state¶

The Features state for the device

struct cxl_features_state {    struct cxl_dev_state *cxlds;    struct cxl_feat_entries {        int num_features;        int num_user_features;        struct cxl_feat_entry ent[] ;    } *entries;};